a. Field of the Invention
This invention relates to improvements in blister sealing machines and in particular to improvements in blister sealing machines of the type disclosed in Australian patent application No. 67,582/74 in the name of Hobosch Pty. Ltd., which are used to heat seal packaging where a product is to be held on a backing, such as of cardboard, by means of a formed member (blister) such as of transparent material adapted to over-lie the article. The improvement concerns the way of mounting of heating means on a plate member which is used to support the formed member (blister) and the backing while the two are heat sealed together.
B. Description of Prior Art
In known blister sealing machines such as disclosed in U.S. Pat. No. 3,170,275 to Rohdin et al. sheet like heater elements are rigidly held over their entire length to a plate member which supports the packaging components during sealing. Generally such plate member has a plurality of rectangular openings therein which receive a formed member (blister) of generally rectangular cup shape, and peripheral flanges on the formed members extend over the heater elements which surround the periphery of the rectangular openings. During manufacture of the plate means Teflon (Registered Trade Mark) impregnated glass cloth or like material is first glued to the plate members so as to cover all surfaces. The heater elements of strip sheet material are then glued to the Teflon (Registered Trade Mark) impregnated material about the periphery of the openings and then a further sheet of Teflon (Registered Trade Mark) impregnated material is glued over the first sheet and to the heater elements. The Teflon (Registered Trade Mark) material coatings are used so that during sealing of the packaging components, they will not bond to the plate means.
It has been found that when the heater elements are used, they expand considerably and because they are rigidly held to the plate means over their whole length by the glue on the Teflon (Registered Trade Mark) material, they tear free in certain areas and they then buckle considerably. Sealing of the package components with buckled heater elements is undesirable because not only does it result in uneven sealing around the periphery of the packaging but it prevents correct alignment of the former member (blister) with respect to its backing as the buckled heater elements usually extend above the height of locating pins on the plate member. Such locating pins are used to align the packaging components with one another over the heater elements. This in turn reduces productivity as considerable time must be spent by operators to correctly align the components.